Examples of conventional methods for tumor (cancer) treatment include treatment methods using chemical anticancer agents or radiation. However, the cancer treatment using anticancer agents, radiation, or the like dose not produce sufficient therapeutic effects. One reason therefor may be that cancer tissues are placed in a hypoxic environment. Although attempts such as hyperthermia and hyperbaric oxygenation have been made as methods for controlling this hypoxic environment, sufficient therapeutic effects have not been established yet. Moreover, reduction in drug activity caused by inappropriate drug distribution is responsible for the mechanism underlying resistance to anticancer agents. In this event, the structural or functional abnormality of tumor vessels is probably involved. To solve these problems, treatment based on immunotherapy in combination with a drug delivery system using nanoparticles, micelle, or the like has been practiced as a conventional technique.
On the other hand, endothelial progenitor cells obtained from bone marrow or the like are cells responsible for revascularization (see e.g., Non-Patent Document 1). For revascularization therapy, autologous endothelial progenitor cells are transplanted to patients with ischemic heart disease or arterial occlusive disease (see e.g., Non-Patent Documents 2 to 4). The endothelial progenitor cells can be separated and collected from bone marrow as well as from peripheral blood, cord blood, or the like. These cells are characterized by having surface markers, for example, CD34 or VEGFR2 (FLK-1), and can be separated from mononuclear cells using magnetic beads or flow cytometry. Likewise, these cells can also be collected as adherent cells obtained by culturing mononuclear cells using an endothelial differentiation medium containing cytokines such as VEGF. These adherent cells are characterized by having uptake of acetylated low-density lipoprotein (acetylated LDL) and being capable of binding to lectin. CD34-positive mononuclear cells obtained from bone marrow are mainly used in the revascularization therapy currently performed using the endothelial progenitor cells.
Animal experiments related to cancer treatment strategy have been reported, in which mouse endothelial progenitor cells obtained from bone marrow or the like, or rat-derived endothelial progenitor cell-like cells are genetically modified and used as carriers (see e.g., Non-Patent Document 5). However, the document discloses that tumor growth was observed in cancer-bearing animals having the transplanted rat-derived endothelial progenitor cell-like cells (immortalized cells). Thus, the use of such immortalized cells in cancer treatment raises serious concerns.
Other methods have been reported, including: a method for preparing mouse endothelial progenitor cells as adherent cells from mouse bone marrow cells (see e.g., Non-Patent Document 6); a method comprising: preparing endothelial progenitor cells from a mononuclear cell fraction collected from the bone marrow of transgenic mice carrying an introduced large T-antigen gene of a temperature-sensitive mutant tsA58 of SV40; subsequently differentiating these endothelial progenitor cells into endothelial cells by culture; and subculturing the differentiated endothelial cells to establish an immortalized endothelial cell strain which has acetylated LDL uptake activities and expresses VEGF (vascular endothelial growth factor) receptor 1, TIE1, and TIE2 (see e.g., Patent Document 1); a method comprising coculturing, in a contact state, undifferentiated bone marrow cells and cells highly expressing Notch ligands such as Jagged-1 or Delta-4 to induce the differentiation of the undifferentiated bone marrow cells into endothelial progenitor cell-like cells (see e.g., Patent Document 2); and a revascularization method comprising: passing a cell suspension containing endothelial progenitor cells and contaminating cells, through a cell separation filter that substantially permits passage of at least the contaminating cells therethrough and substantially captures the endothelial progenitor cells; introducing a fluid into the cell separation filter to collect the endothelial progenitor cells captured by the cell separation filter; and using the collected endothelial progenitor cells in revascularization (Patent Document 3).    Patent Document 1: Japanese Patent Laid-Open No. 2001-231549    Patent Document 2: Japanese Patent Laid-Open No. 2007-89536    Patent Document 3: Japanese Patent Laid-Open No. 2003-250820    Non-Patent Document 1: Asahara T, et al: Science 275; 964-967, 1997    Non-Patent Document 2: Assmus B, et al: Circulation 106; 3009-3017, 2002    Non-Patent Document 3: Asahara T, et al: Experimental Medicine, vol. 24, No. 1, p. 30-36, 2006    Non-Patent Document 4: Ii M, et al: Experimental Medicine, vol. 24, No. 18, p. 2871-2879, 2006    Non-Patent Document 5: Muta M, et al: Oncology Report 10; 1765-1769, 2003    Non-Patent Document 6: Ii M, et al: Circulation Research 98; 697-704, 2006